Powders, test methods sedimentation

In the United States, a number of physical tests are performed on siUcon carbide using standard AGA-approved methods, including particle size (sieve) analysis, bulk density, capillarity (wettabiUty), friabiUty, and sedimentation. Specifications for particle size depend on the use for example, coated abrasive requirements (134) are different from the requirements for general industrial abrasives. In Europe and Japan, requirements are again set by ISO and JSA, respectively. Standards for industrial grain are approximately the same as in the United States, but sizing standards are different for both coated abrasives and powders. 

Sulcer and Denson (Ref 19) used the gas chromatographic—B .T. procedure for the analysis of Class I A1 powder (45 u max dia) which cannot be tested satisfactorily by sedimentation methods because of the presence of aggregates. A rough statistical evaluation of this procedure was made by running twelve determinations and calculating the standard deviation as shown in Table 14 ... 

Eor total metal solubilization a representative unfrozen sample of 0.5 g, dried at 110°C and finely powdered, is dissolved in a Teflon bomb by an acid mixture of 5 ml of 40% HE, 1 ml of aqua regia (HNO3-HCI 1 3 v/v) and 5 ml of MQ water, heated at 180°C for 90 min and then cooled to room temperature. 5 ml of saturated H3BO3 solution are then added to the Teflon bomb and, after dilution to 50 ml in a volumetric flask, the solution is analyzed by ICP-AES. To test the accuracy of the total solubilization method several certified reference materials in sediment matrices are always analyzed along with the unknowns, obtaining results in a good agreement with certified values, as reported in Table 8.2. 

The advantage of the photosedimentometer is that sedimentation is not disturbed by taking samples for the measurement of concentration. Furthermore, of all methods of analysis, this apparatus requires the smallest amount of the powder to be analyzed. In some instruments the duration of the test can be shortened by reducing the height of sedimentation during measurement of the finer particle fraction another possibility to carry out sedimentation analyses more rapidly is the use of a scanning (X-ray) beam. 

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